unique_ptr overview, common operations, deleter

1. Overview of unique_ptr

1.1 Introduction to unique_ptr

             unique_ptr is a smart pointer defined in <memory> since C ++ 11. It holds the exclusive right to the object, that is, two unique_ptr can not point to an object, can not be copied operation can only be moved.

1.2 Initialization of unique_ptr

	//常规初始化
	unique_ptr<int> up(new int(100));

	//make_unique 初始化
	unique_ptr<int> up1 = make_unique<int>(100);  //C++14中才出现
	auto up2 = make_unique<int>(100);

Two. Unique_ptr common operations

2.1 Operation not supported by unique_ptr

	unique_ptr<int> up(new int(100));

	/*

	unique_ptr<int> up2 = up;

	unique_ptr<int> up3(up);

	unique_ptr<int> up4;
	up4 = up;

	*/

2.2 Mobile semantics

#include <iostream>
using namespace std;

unique_ptr<int> func()
{
	return unique_ptr<int>(new int(100));
}

int main()
{

	//第一种接收从函数返回的临时对象
	unique_ptr<int> up = func();

	//第二种使用move函数
	unique_ptr<int> up2(new int(100));
	unique_ptr<int> up3 = move(up2);  //此时up2指向空，up3指向原来up2指向的内存

	return 0;
}

2.3  release

	unique_ptr<int> up(new int(100);

	unique_ptr<int> up2(up.release());  //release 切断智能指针与所指对象的联系，并返回裸指针

2.4  reset

	//1.reset不带参数：释放所指对象资源，并将指针指向空
	unique_ptr<int> up(new int(100));
	up.reset();
	if (!up)
	{
		cout << "up是空指针" << endl;
	}

	//2.reset带参数：释放智能指针所指的对象并将智能指针指向参数
	unique_ptr<int> up1(new int(100));
	up1.reset(new int(101));
	if (up1)
	{
		cout << "up1不为空" << endl;
	}

2.5 = nullptr frees resources and sets null pointer

	unique_ptr<int> up(new int(100));
	up = nullptr;

2.6 Point to an array

	unique_ptr<int[]> up(new int[10]);  //如果指向一个数组，<>中需要带上 []，否则将导致内存泄漏以及不可以使用下面的[]索引
	up[1] = 100;

2.7  get

	unique_ptr<int> up(new int(100));
	int * p = up.get();  //返回裸指针

2.8 * Dereference

	unique_ptr<int> up(new int(100));
	cout << "up的值：" << *up << endl;

2.9  swap

	unique_ptr<int> up(new int(100));
	unique_ptr<int> up2(new int(9));

	//swap的作用：交换两个智能指针所指向的对象
	swap(up, up2);  //第一种调用方式
	cout << "up的值：" << *up << endl;
	up.swap(up2);  //第二种调用方式
	cout << "up的值：" << *up << endl;

2.10 Convert unique_ptr to shared_ptr

#include <iostream>
using namespace std;

unique_ptr<int> func()
{
	return unique_ptr<int>(new int(100));
}

int main()
{

	//如果unique_ptr作为右值，可以将其转换为shared_ptr
	
	//第一种
	unique_ptr<int> up(new int(100));
	shared_ptr<int> sp = move(up);

	//第二种
	shared_ptr<int> sp1 = func();

	return 0;
}

3. Remover

3.1 Specified deleter

#include <iostream>
using namespace std;

void mydelete(int *p)
{
	delete p;
	p = nullptr;
	cout << "内存已经被释放" << endl;
}

int main()
{
	typedef void(*fp)(int*);
	unique_ptr<int, fp> up(new int(100), mydelete);

	//uniqeu_ptr指定删除器总结：
		//需要在<>中指定函数类型
	    //因为需要在<>指定函数类型，所以unique_ptr的灵活性受到了限制，不同的函数类型使得unique_ptr的类型不同，类型不同就不可以放在同一个容器中

	return 0;
}